In a new deployment for Odoo11EE , the backup file size in doubling each month, is this considered normal? 

The average daily transactions is around 50 invoices, sales orders, ...etc. No images are being uploaded. 

odoodb_2017-12-08.zip  7MB
odoodb_2018-01-03.zip  13MB
odoodb_2018-01-31.zip  25MB
odoodb_2017-02-13.zip  52MB
odoodb_2017-02-22.zip  78MB
odoodb_2017-03-19.zip  157MB
odoodb_2017-04-08.zip  244MB
odoodb_2017-05-09.zip  374MB